This project proposal is prompted by the problem of liquid storage of human platelets at 4 degrees C. Current evidence suggests that the cold-induced shape change of platelets, apparently responsible for their decreased viability on reinfusion, is due to disruption of the marginal bundle of microtubules (MT). We therefore propose to study biochemical and biophysical aspects of platelet MT in terms of their physiological role in platelet function and with respect to the determinants of their structural integrity. The major areas of investigation are: 1) factors involved in the reversible assembly-disassembly of platelet MT (particularly the temperature-dependent process), 2) development of methods for preserving the structural organization of platelet MT during 4 degrees C storage, 3) interaction of contractile proteins and membrane polypeptides with platelet MT, and 4) the role of MT in aggregation and other contractile platelet activities. The successful preparation of monospecific antibody to platelet tubulin allows us to isolate this protein by immunosorption rapdily, in good yield and in highly pure form. There are 3 principal reasons for choosing platelets rather than tissues of higher tubulin content for our studies: 1) the special function of MT in platelets, 2) the species differences which exist between tubulins from different sources and 3) the ability to follow changes in MT assembly directly in intact platelets by measurement of light scattering. The proposed studies are to be conducted partly with intact platelets and partly with isolated MT protein. The main thrust of this project will be directed towards elucidation of the factors operative in the temperature-dependent polymerization-depolymerization process of platelet tubulin and subsequently in the development of techniques which might stabilize MT during 4 degrees C storage of platelets.